1 chapter 2 primitive data types and operations f introduce programming with an example the myinput...

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Chapter 2 Primitive Data Types and Operations

Introduce Programming with an Example The MyInput class Identifiers, Variables, and Constants Primitive Data Types

– Byte, short, int, long, float, double, char, boolean Expressions Operators, Precedence, Associativity, Operand

Evaluation Order: ++, --, *, /, %, +=, -=, *=, /=, %=, ^, &, |, +, -,

Style and Documentation Syntax Errors, Runtime Errors, and Logic Errors

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Introducing Programming with an Example

Example 2.1 Computing the Area of a Circle

This program reads the radius from the keyboard and computes the area of the circle.

ComputeAreaComputeArea RunRun

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The MyInput Class

MyInputMyInput

This class contains the methods for reading an int, a double, or a string from the keyboard.

The methods are readInt, readDouble, and readString

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Identifiers An identifier must start with a letter, an underscore, or a

dollar sign. An identifier cannot contain operators, such as

+, -, and so on. An identifier cannot be a reserved word. (See Appendix

A, “Java Keywords,” for a list of reserved words). An identifier cannot be true, false, ornull.

An identifier can be of any length.

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Variables

// Compute the first arearadius = 1.0;area = radius*radius*3.14159;System.out.println("The area is “ + area + " for radius "+radius);

// Compute the second arearadius = 2.0;area = radius*radius*3.14159;System.out.println("The area is “ + area + " for radius "+radius);

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Declaring Variablesint x; // Declare x to be an // integer variable;

double radius; // Declare radius to // be a double variable;

char a; // Declare a to be a // character variable;

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Assignment Statements

x = 1; // Assign 1 to x;

radius = 1.0; // Assign 1.0 to radius;

a = 'A'; // Assign 'A' to a;

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Declaring and Initializingin One Step

int x = 1;

double d = 1.4;

float f = 1.4;

Is this statement correct?

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Constants

final datatype CONSTANTNAME = VALUE;

final double PI = 3.14159;

final int SIZE = 3;

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Numerical Data Types

byte 8 bits

short 16 bits

int 32 bits

long 64 bits

float 32 bits

double 64 bits

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Number Literals int i = 34;

long l = 1000000;

float f = 100.2f; orfloat f = 100.2F;

double d = 100.2d ordouble d = 100.2D;

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Operators

+, -, *, /, and %

5/2 yields an integer 2.

5.0/2 yields a double value 2.5

5 % 2 yields 1 (the remainder of the division)

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Shortcut Operators

Operator Example Equivalent

+= i+=8 i = i+8

-= f-=8.0 f = f-8.0

*= i*=8 i = i*8

/= i/=8 i = i/8

%= i%=8 i = i%8

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Increment andDecrement Operators

x = 1;

y = 1 + x++;

y = 1 + ++x;

y = 1 + x--;

y = 1 + --x;

Using increment and decrement operators makes expressions short, but it also makes them complex and difficult to read. Avoid using these operators in expressions that modify multiple variables, or the same variable for multiple times such as this: int k = ++i + i.

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Assignment Expressions and Assignment Statements

Prior to Java 2, all the expressions can be used as statements. Since Java 2, only the following types of expressions can be statements:

variable op= expression; // Where op is +, -, *, /, or %

++variable;variable++;--variable;variable--;

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Numeric Type Conversion

Consider the following statements:

byte i = 100;

long l = i*3+4;

double d = i*3.1+l/2;

int x = l; (Wrong)

long l = x;(fine,implicit casting)

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Type Casting

double float long int short byte

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Type Casting, cont.

Implicit casting

double d = 3; (type widening)

Explicit casting

int i = (int)3.0; (type narrowing)

What is wrong? int x = 5/2.0;

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Character Data Type

char letter = 'A'; (ASCII)

char numChar = '4'; (ASCII)

char letter = '\u000A'; (Unicode)

char letter = '\u000A'; (Unicode)

Special characters

char tab = ‘\t’;

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Unicode Format

Description Escape Sequence Unicode

Backspace \b \u0008

Tab \t \u0009

Linefeed \n \u000a

Carriage return \r \u000d

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The boolean Type and Operators

boolean lightsOn = true;

boolean lightsOn = false;

&& (and) (1 < x) && (x < 100) || (or) (lightsOn) || (isDayTime) ! (not) !(isStopped)

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The & and | Operators

If x is 1, what is x after this expression?

(1 > x) & ( 1 > x++)

If x is 1, what is x after this expression?

(1 > x) && ( 1 > x++)

How about (1 = x) | (1 > x++)?(1 = x) || (1 > x++)?

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Operator Precedence var++, var— ++var,--var Casting ! *, /, % +, - <, <=, >, >= ==, !=; & ^ | && || =, +=, -=, *=, /=, %=

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Operator Associativity

When two operators with the same precedence are evaluated, the associativity of the operators determines the order of evaluation. All binary operators except assignment operators are left-associative.

a + b – c – d is equivalent to  ((a – b) + c) – d

Assignment operators are right-associative. Therefore, the expression

a = b += c = 5 is equivalent to a = (b += (c = 5))

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Programming Style and Documentation

Appropriate Comments Naming Conventions Proper Indentation and Spacing Lines Block Styles

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Appropriate Comments

Include a summary at the beginning of the program to explain what the program does, its key features, its supporting data structures, and any unique techniques it uses.

Include your name, class section, instruction, date, and a brief description at the beginning of the program.

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Naming Conventions

Choose meaning and descriptive names. Variables and method names:

– Use lowercase. If the name consists of several words, concatenate all in one, use lowercase for the first word, and capitalize the first letter of each subsequent word in the name. For example, the variables radius and area, and the method computeArea.

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Naming Conventions, cont.

Class names: – Capitalize the first letter of each

word in the name. For example, the class name ComputeArea.

Constants: – Capitalize all letters in constants.

For example, the constant PI.

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Proper Indentation and Spacing

Indentation– Indent two spaces.

Spacing – Use blank line to separate segments of the code.

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Block Styles

Use next-line style for braces.

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Programming Errors

Syntax Errors– Detected by the compiler

Runtime Errors– Causes the program to abort

Logic Errors– Produces incorrect result

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Example 2.2 Computing Mortgages

ComputeMortgageComputeMortgage RunRun

This program lets the user enter the interest rate, number of years, and loan amount and computes monthly payment and total payment.

12)1(11

numOfYearserestRatemonthlyInt

erestRatemonthlyIntloanAmount

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Example 2.3 Computing Changes

This program lets the user enter the amount in decimal representing dollars and cents and output a report listing the monetary equivalent in single dollars, quarters, dimes, nickels, and pennies. Your program should report maximum number of dollars, then the maximum number of quarters, and so on, in this order.

ComputeChangeComputeChange RunRun